The present application relates to a display apparatus which includes a white light source.
Together with the progress of the semiconductor technology, a thin display apparatus called FPD (Flat Panel Display) has been developed and spread widely.
Various principles of light emission are applied to such thin display apparatus such as an organic EL (Electro Luminescence) display apparatus and a plasma display apparatus, and researches for such various thin display apparatus are proceeding.
Particularly, a liquid crystal display apparatus was placed into practical use earlier than display apparatus of the other types and has been popularized widely. Thus, a demand for an enhanced display characteristic (picture quality) of the liquid crystal display apparatus is increasing.
As regards a liquid crystal display apparatus, attention is paid particularly to the color reproduction performance among various display characteristics. The color reproduction performance enhances, that is, chromaticity points can be covered over a wider area, as light emission spectra corresponding to the colors of blue, green, and red are narrowed. However, as the light emission spectra are narrowed, the luminance decreases because the light emission center wavelength is displaced away from 555 nm at which the sensitivity of distinct vision is highest and the spectrum width is narrowed. In other words, the luminance and the color reproduction performance have a tradeoff relationship to each other.
In recent years, also a display apparatus has been proposed which is directed to increase of chromaticity points, which can be covered, in order to achieve a higher color reproduction performance. A display apparatus of the type described is disclosed, for example, in Japanese Patent Laid-open No. 2004-163902. However, enhancement of the color reproduction performance of a display apparatus involves decrease of the luminance as described above. Besides, in recent years, an apparatus configuration which can cover a particular chromaticity point with certainty is frequently demanded as a useful configuration rather than another apparatus configuration which simply increases chromaticity points which can be covered.
For example, the sRGB standards were established as international standards (IEC61966-2-1) in 1999. The sRGB standards are unified standards which reduce or eliminate differences in color reproduction performance among different types of apparatus such as display apparatus beginning with television sets, digital still cameras, printers, and mobile apparatus. The sRGB standards make image color information represented by a mobile apparatus and image color information represented by an inputting and outputting device coincide with each other to achieve unification (matching in color reproduction performance) of the color reproduction performance and the color space which differ extremely depending upon the maker or the model of the apparatus. However, it is considered difficult for a liquid crystal display apparatus, particularly a liquid crystal display apparatus in which a cold cathode fluorescent lamp (CCFL) is used as a backlight system, to assure a color reproduction performance which covers a particular chromaticity point prescribed in the sRGB standards, for example, a green chromaticity point of (0.300, 0.600).
At present, for fluorescent materials to be used for a liquid crystal display apparatus which includes a cold cathode fluorescent lamp as a backlight, BAM:Eu having a composition represented by a [Chemical formula 5] given below is available as a blue fluorescent material; LAP (lanthanum phosphate terbium) having a configuration represented by a [Chemical formula 6] given below is available as a green fluorescent material; and YO having a composition represented by a [Chemical formula 7] given below is available as a red fluorescent material:BaMgAl10O17:Eu  [Chemical formula 5]LaPO4:Ce, Tb  [Chemical formula 6]Y2O3:Eu  [Chemical formula 7]
A verification test of a green chromaticity point was conducted for three different liquid crystal display apparatus on the market which incorporate the fluorescent materials specified above. In FIG. 9, chromaticity points (ranges) which can be covered by the liquid crystal display apparatus are indicated by a solid line graph l, a broken line graph m, and a chain line graph n. As seen from the graphs l, m, and n, they are closest, for example, at chromaticity points (0.2786, 0.6053), (0.2632, 0.5985), and (0.2808, 0.5899) to the green chromaticity point prescribed by the sRGB standards. Therefore, it was confirmed that the particular chromaticity point is not covered.
Such a problem of a display apparatus as just described arises from a fact that, for example, when blue or red light enters a color filter of a pixel corresponding to green light, a green output chromaticity point is displaced in such a manner as to be dragged to the blue side or the red side. It is considered very difficult to solve this problem because light emission spectra of the fluorescent materials of red, green, and blue partly overlap with each other and the problem is complicated by a mutual relationship of the spectra with color filters which construct the display apparatus.
Accordingly, in order to achieve enhancement of the color reproduction performance while a sufficient luminance is maintained, it is considered particularly preferable to cover a particular chromaticity point, for example, the green chromaticity point prescribed by the sRGB standards, rather than to merely achieve increase of chromaticity points.